Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $59.81   11.381%   $66.617   $66.62   $66.60   $66.60  
  Purchase #2 $86.57   9.741%   $95.0028   $95.00   $95.00   $95.00  
  Purchase #3 $148.89   5.658%   $157.3142   $157.31   $157.30   $157.30  
  Purchase #4 $239.85   11.492%   $267.4136   $267.41   $267.40   $267.40  
  Purchase #5 $63.87   3.517%   $66.1163   $66.12   $66.10   $66.10  
  Purchase #6 $162.65   9.218%   $177.6431   $177.64   $177.65   $177.60  
  Purchase #7 $249.53   6.624%   $266.0589   $266.06   $266.05   $266.10  
  7 purchase totals = $1,011.17       $1,096.1659   $1,096.16   $1,096.10   $1,096.10